The present invention relates to an active pull-up circuit, and more particularly to an active pull-up circuit suitable for a dynamic memory circuit composed of field effect transistors.
Active pull-up circuits have been advantageously utilized in dynamic circuits, especially in dynamic memories in order to establish potentials equal to or above power supply voltages at predetermined circuit nodes. For example, in a dynamic memory, an active pull-up circuit is provided for each bit line. In this memory, a read-out signal produced on a bit line is once distinguished as one of the binary logic levels by a sense amplifier and thereafter in the case where the read-out signal is high, the potential of that bit line is pulled-up to in above a power supply voltage (Vcc) by the active pull-up circuit so that the pulled-up potential on that bit line is re-written into the addressed memory cell, as well as being taken out to an output circuit. In dynamic memories, active pull-up circuits must be provided for the respective bit lines and hence the number of the active pull-up circuits has become very large because of the recent increase in memory capacity of dynamic memories. Therefore, the whole area occupied by the active pull-up circuits and the whole power consumption caused by the active pull-up circuits in a dynamic memory have become important in evaluating a memory. For example, the typical, prior art active pull-up circuit is composed of four field effect transistors and a capacitor and is adapted to operate by two or more control signals. Therefore, it has been difficult to fabricate such prior art active pull-up circuits in the memory chip with ease.